Chapter 13 The search for plant-derived compounds with antifeedant activity

Abstract

There are many thousands of plants for which further research is needed to understand the role secondary metabolites play in insect–plant interactions, especially their role in the modulation of insect host selection and feeding behavior. The presence of a specific group of compounds in a plant can elicit behavioral responses from insects that vary from a stimulant to a deterrent. The deterrents or antifeedants usually signals the unsuitability of a plant allowing the insect to reject on contact, and thus avoiding the ingestion of compounds that could be toxic. In most cases it is the ovipositioning female that selects the host plant for the larvae but for mobile insects, such as locusts, the nymphs select their food as they move through the vegetation. When the insect encounters a potential host plant, its selection behavior will be influenced by its ability to detect compounds in the plant. Despite the amount of research already undertaken on insect selection behavior, researchers still do not fully understand the taste sensilla that are used by an insect to taste its food and are of primary importance in enabling an insect detect antifeedants. When the compounds in the plant stimulate the taste neurons, they produce electrical impulses that transmit the neural code, which can result in the modification of insect behavior. The behavioral and neural response of an insect to a specific compound is not always fixed. Thus, host selection is not a fixed response and the variability in the behavior of an individual will be influenced by its own experience as well as genetic or functional factors such as the expression of receptors on taste neurons that are stimulated by specific compounds.